Sanitary-bacteriological monitoring of water quality in Lake Baikal – from single/one-off studies to systematic annual expeditions

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1. Introduction

The surface waters of our planet, including lakes, reservoirs, and rivers, as well as seas and oceans, are subject to constant anthropogenic impact. The ecosystem of Lake Baikal, which was included in the UNESCO World Natural Heritage List in 1996 due to the uniqueness and purity of its waters, has not escaped this impact. The ecological condition of fresh water bodies – the main sources of drinking water – is degrading worldwide, which leads to the disruption of evolutionary microbiocenoses and the development of opportunistic and pathogenic bacteria in them. Because of their unusual competitive ability, developed over 3 billion years of existence, microorganisms can inhabit all ecological niches, from polar regions to deserts. Water is one of the most favorable habitats for them; in aquatic ecosystems, microorganisms reach high numbers, being determining and necessary links in the cycle of chemical elements, providing the process of continuous creation and destruction of organic substances as a result of interconnected functioning.

Microbiological studies of the Baikal water and sediments have been carried out for about 100 years (Yasnitsky et al., 1927; Nechaeva and Salimovskaya-Rodina, 1935; Kuznetsov, 1951; Romanova, 1958; et al.). In the following years, abundance and biomass of bacterioplankton were studied not only in the southern part of the lake but also throughout the Baikal water area. Their interannual dynamics and vertical distribution, peaks in seasonal development, correlations with the dynamics of abundance and composition of phytoplankton, and changes in water temperature were established, the time of bacterial generation was determined, and work on identification of the species composition of cultured microbial communities was started (Egorova et al., 1952; Rodina, 1954; Kuznetsov, 1957; Kriss and Chebotarev, 1970). During this period of microbiology formation in Lake Baikal, the microbiologists from research institutions in Moscow and Leningrad played the main role, using their knowledge and experience.

Sanitary-bacteriological assessment of water quality implies the determination of a set of sanitary indicators – criteria reflecting the sanitary condition of the water body under study – in accordance with the requirements of regulatory documents. Sanitary indicators are fecal indicator bacteria (FIB). They are used worldwide to detect and prevent fecal contamination and associated risks to human health due to the likely presence of pathogenic bacteria and viruses. FIB include bacterial groups such as total coliform bacteria (TCB), thermotolerant coliform bacteria (TCB), fecal coliform bacteria (fecal coliforms), E. coli, Enterococci, Bifidobacterium, Bacteroides, and Clostridium spp., which are widely distributed in the feces of humans and most animals. Their levels in wastewater and feces are relatively high, so they are usually detected when fecal pollution is present in surface waters. Therefore, surface waters are monitored using the FIB abundance, for which standards are set by legislative documents for assessing the quality of the waters used. Such water quality studies were initiated much later in Lake Baikal.

2. Materials and methods

After the reorganization of Baikal Limnological Station into Limnological Institute of the Siberian Branch of the USSR Academy of Sciences in 1961 and the foundation of the “Laboratory of Applied Microbiology” in 1972, headed by M.A. Messineva (Cand. Sc. Biology), who investigated microorganisms of sediments in Lake Baikal in the 1950s (Messineva, 1957), research of microorganisms of Lake Baikal became planned, systematic, and comprehensive. Since the purpose of our work is to analyze the conducted studies on sanitary-bacteriological monitoring of Lake Baikal water quality for the previous period of work and to develop a scheme of it for the unique oligotrophic water body, we do not list all microbiological works, as they are available on the website of Limnological Institute Siberian Branch of the Russian Academy of Sciences, as well as in the monograph-summary of microbiological studies of water bodies and watercourses of the Baikal-Angaro-Yenisei hydrosystem (Vinogradova et al., 2004).

In 2023, the Government of the Russian Federation approved a new Resolution No. 260 “Regulations on State Environmental Monitoring of the Unique Ecological System of Lake Baikal”, in which it established the procedure for its implementation. In paragraphs 8 “d” and 11 “e” it is obliged to provide information to “the federal state budgetary institution “Siberian Branch of the Russian Academy of Sciences” in terms of the results of observations of the state of Lake Baikal”. In order to assess the previously conducted volumes and periodicity of research on sanitary-bacteriological monitoring of the Baikal ecosystem, as well as to discuss the current use of specific standard and new indicators, research methods, water sampling stations, seasons, and the frequency of their sampling, which is necessary for the development and implementation of the scheme of microbiological monitoring itself, we have analyzed the available published set of sanitary-bacteriological studies of the lake.

3. Results and discussion

The analysis of the results of sanitary-bacteriological studies of Lake Baikal showed that in this scientific direction, single works started in connection with the construction of the Baikal Pulp and Paper Mill (BPPM) only in the late 1960s of the last century. Microbial communities of water and polluted sediment in the area of the BPPM wastewater influence were first described in 1970–1973 in the works of G.A. Goman (1973). Works were then carried out in this area to assess the abundance of anaerobic saprophytes, sulfate reducers, and methanogens; rates of protein decomposition, cellulose decomposition, sulfate reduction, and methane formation were determined; and a forecast was made about the deterioration of the ecological situation in case of further wastewater discharge (Namsaraev et al., 1995; Zemskaya et al., 1997).

The water quality of Southern Baikal and, mainly, near the B. Koty settlement and the Baikalsk town was investigated during this period by scientists of Research Institute of Biology of Irkutsk State University (Maksimova and Maksimov, 1989). Long-term results of these authors` studies showed stable differences in the Baikal water quality during all periods: at the station “1 km from the shore” of the B. Koty settlement, remote from industrial and agricultural zones, water quality at all depths was high, while near the Baikalsk town within a radius of up to 10 km at all depths, water did not meet standards for drinking water, recreational, and fishery activities.

In 1993, the researchers of Limnological Institute SB RAS, V.V. Drucker, T.Y. Kostornova, O.A. Molozhavaya, and V.A. Afanasiev, started and completed an assessment of the water quality in the littoral and pelagic zones of the whole Lake Baikal up to maximum depths using sanitary-bacteriological indicators. It has been found that the lake pelagic zone has high water quality both at the surface and at all depths. Coastal waters near all settlements have low quality, and E. coli are detected in many samples. At the same time, microbiological monitoring of the major tributaries of Lake Baikal began to be conducted, which showed poor water quality in the estuaries of the Selenga, Barguzin, Bolshaya Goloustnaya, Turka, Tyya, Pereemnaya, and Pokhabikha rivers entering the lake in spring (Drucker and Maslenikov, 1998).

To determine the scope of distribution and identify opportunistic bacteria in the water of Lake Baikal throughout its water area, the staff of the Laboratory of Aquatic Microbiology of LIN SB RAS conducted for the first time the intentional long-term studies in different seasons of the year between 1997 and 2000 (Drucker and Panasyuk, 2002; Panasyuk and Drucker, 2002). Water samples were taken along standard hydrological transects at the central deep stations at different horizons and at the coastal stations near the western and eastern shores: 1. Maritui settlement – Solzan settlement; 2. Listvyanka settlement – Tankhoi settlement; 3. Kadilny Cape – Mishikha settlement; 4. Kharauz Strait – Krasny Yar Cape; 5. Anga River – Sukhaya River 6. Boldakova River - Olkhonskiye Vorota Strait; 7. Ukhan Cape – Tonkii Cape; 8. Pokoyniki Cape – Ushkan Cape; 9. Elokhin Cape - Davsha settlement; 10. Kotel`nikovskii Cape – Amnundakan Cape; 11. Baikal`skoe village – Turali Cape; 12. Zavorotny Cape – Sosnovka River; 13. Krestovy Cape – Khoboy Cape; 14. Tyya River – Nemnyanka River.

As a result of the studies, 898 strains of potentially pathogenic bacteria (PPB) were isolated in the littoral zone of the lake, which are representatives of 31 species belonging to the Enterobacteriacae family and non-fermenting group of bacteria. The number of studied bacteria increased in the water during the summer and autumn periods and decreased during the winter months. Opportunistic bacteria were unevenly distributed throughout the lake`s water area, and their populations increased significantly at the locations where untreated wastewater from different sources was dumped. The greatest abundance and species diversity of this group of bacteria are found in the water of Southern Baikal – the Listvyanka settlement, Port Baikal settlement, Baikalsk town; in Central Baikal – Barguzin and Chivyrkuy bays, the Selenga river delta, and Maloe More strait; in Northern Baikal – a section of the Baikal-Amur railway. The studied group of bacteria was not found throughout the entire water column in the pelagic zone of the lake at various sites (more than 30 stations). The dominant species of opportunistic bacteria isolated from the littoral waters of the lake were Pseudomonas aeruginosa, Enterobacter cloacae, Citrobacter freundii, and Burkhalderia cepacia. The opportunistic bacteria isolated from the Lake Baikal waters have multiple antibiotic resistances, hemolytic activity in human erythrocytes, the ability to cultivate at 37°C, and, therefore, carry a potential epidemiological hazard to public health (Drucker and Panasyuk, 2006). The authors proposed to use additionally for sanitary-bacteriological control of the Baikal water quality the detected potential-pathogenic bacteria, as well as bacteria of the Enterococcus genus: E. faecium, E. avium, E. faecalis, E. mundtii, E. hirae, E. durans, and E. gallinarum, as specific indicators of fecal (untreated) water inflow into the lake. Long-term studies have established that the main sources of pollution in the Baikal waters are untreated domestic wastewater from settlements located on the shores of the lake, agricultural enterprises, and tourist complexes, which do not have systems of disinfection, utilization, and removal of wastewater, as well as the increasing number of tourist boats, which do not have tanks for collecting domestic and bilge waters.

In 2000-2009, there was a trend towards an increase in sanitary-bacteriological indicators in water in the area of discharge of “decontaminated” wastewater from the Baikal Pulp and Paper Mill (Shchetinina et al., 2013). In view of the deteriorating sanitary situation, the authors of the paper conducted studies on the diversity and antibiotic resistance of bacteria isolated from water in the most anthropogenically influenced areas of the lake. Other authors have also found representatives of sanitary-bacteriological pollution – bacteria of the Enterococcus genus in the water of different areas of Lake Baikal (Kravchenko, 2009).

In addition to these microorganisms, toxic cyanobacteria that are harmful to humans were discovered in Lake Baikal water for the first time in Russia during that time (Tikhonova, 2006; Belykh et al., 2013; Belykh et al., 2015). Different types and variants of toxins and the genes that produce them were studied. This new factor is crucial for the sanitary-bacteriological monitoring of the Baikal water quality because cyanobacterial blooms, which are currently the most significant and recognizable effects of eutrophication in water bodies worldwide, are already happening in various regions of Lake Baikal. The concentrations of microcystins and saxitoxins in samples of plankton and benthos from the lake were determined, and the degree of hazard of toxic cyanobacteria to human and animal health was assessed. It is shown that “blooming” of benthic cyanobacteria with the presence of toxin-producing species, which started on Lake Baikal in 2011, have now taken on the character of an ecological crisis and may have caused mass mortality of Baikal sponges (Belykh et al., 2017). In order to address the issue of including these bacteria in the official documentation on microbiological monitoring of the Baikal water quality, these new research findings unquestionably merit a proper evaluation.

In recent years, the Lake Baikal ecosystem has been undergoing serious ecological changes. Signs of eutrophication – intensive development of algae non-specific for the littoral of the lake, mass mortality of sponges, and blooming of toxic cyanobacteria – have been observed in the coastal areas of some regions (Timoshkin et al., 2016). The volume of discharges of poorly treated and untreated wastewater from settlements into the lake is growing, recreational loads are increasing, and the number of tourist vessels not equipped with tanks for collecting domestic and bilge water has sharply increased. The number of tourists coming to Lake Baikal in all seasons of the year has increased manifold. Thus, in 2019, their number reached 2.2 million. More than 40 zones of recreational development have been formed directly on the lake coast, where most of the tourist accommodation facilities are concentrated: camping sites, hotels, and holiday homes. Questions arise: how effectively do septic tanks work in tourist recreation areas without damaging the Baikal ecosystem? How often does “Rosprirodnadzor” check the utilization of household and bilge water on tourist motorboats?

Since 2000, Limnological Institute SB RAS has developed a practice of conducting complex expeditions throughout Lake Baikal, in which microbiologists are constantly involved. It goes without saying that expeditionary work throughout Lake Baikal has been carried out before, but the complexity of the research was limited by the lack of necessary instruments for simultaneous collection of a large number of water and sediment samples, rapid measurement of abiotic parameters to maximum depths, etc. To date, only Limnological Institute has a research fleet equipped with the necessary instruments for scientific limnological studies in Lake Baikal. For this reason, sanitary-bacteriological monitoring of the water quality of Lake Baikal and its tributaries is carried out by the staff of the Laboratory of Aquatic Microbiology of the Institute, which has all necessary modern equipment and separate facilities for sanitary-bacteriological monitoring of the Lake Baikal water quality by classical and modern molecular-biological methods. The Laboratory of Aquatic Microbiology is accredited in the national system of Rosakkreditation (№ RA.RU.21ЛИ02).

Sanitary-bacteriological monitoring of the Baikal water quality carried out during 2010–2023 in the annual spring (second half of May–early June), summer (August), and autumn (second half of September) Circum-Baikal expeditions showed that FIB are constantly present in the coastal part of the lake. Littoral zone of the lake showed a significant amount of coliform bacteria and enterococci in Listvyanka settlement, Baikalsk town, Kultuk settlement – the southern part of the lake; in the waters of the Maloe More and Olkhonskiye Vorota straits and the Selenga delta – the central basin; in the Severobaikalsk town, and the Zarechny settlement – the northern part of the lake (Shtykova et al., 2016, 2018b; Suslova et al., 2017; Podlesnaya et al., 2022). In 2011, exceedance of the regulated water quality standards of the Russian Federation was observed throughout the entire pelagic zone of Lake Baikal, as well as in most of its major tributaries. In 2012 and 2015, an exceedance of sanitary-bacteriological indicators of pelagic waters was observed only in the southern part of the lake (Fig. 1). In September 2016, the maximum share of water samples with a low self-purification coefficient was recorded both in the pelagic zone (60%) and in the river mouths (62.5%).

 

Fig.1. Abundance of sanitary-microbiological indicators in the pelagial water zone of Lake Baikal in 2010-2020 data (j-June, a-August and s-September). Red color –the standards.

 

In the waters of the estuaries of rivers flowing into the lake, the number of sanitary indicatory-groups of bacteria in 2010–2020 was (Fig. 2), on average, by one order more than their content in the pelagic zone – the Goloustnaya, Buguldeika, Turka, Anga, Barguzin, Sukhaya rivers, as well as the Selenga delta (Drucker et al., 2022). The most unfavorable period for water quality was in August 2011 and May-June 2012, when the number of non-standard water samples was highest. In August 2010, May-June 2014, and September 2017, all river samples taken corresponded to “satisfactory” surface water quality indicators.

 

Fig.2. Abundance of sanitary-microbiological indicators in water of the tributaries in 2010-2020 data. Red color –the standards.

 

In 2022-2023, besides the standard sanitary-bacteriological monitoring studies, we tested additional method – detection of fecal contamination using marker probes for bacteria (inhabitants of human and animal intestines), as well as detection of viral communities in water. Moreover, in 2021 the grid of sampling stations included treated wastewater from the treatment facilities of the Slyudyanka and Severobaikalsk towns, analyzed according to SanPiN 1.2.3685-21 “Hygienic standards and requirements to ensure safety and (or) harmlessness of environmental factors for humans”. Also, 10 samples of sediments were taken in the coastal zone at various sites where tourists rest.

The results show notable exceedances of SanPiN norms in both years of the most recent investigations at 55 (170 water samples) and 59 (71 water samples) sites for the primary sanitary-bacteriological indicators. Thus, in 2023 these are the following areas the Baikalsk town, the Babushkin, Listvyanka, Tankhoy, B. Goloustnoye, and Posolsky Sor settlements, Peschanaya and Aya bays, and the bays of Maloe More (Bazarnaya, Kurkutskaya, Mandarkhan, Shida, and Khuzhirsky, Chivyrkuy bay – Kurbulik, Monakhovo, and Arangatui). The highest levels of these bacteria were found in the Babushkin town (E. coli in 1.7 times, enterococci in 20 times), the Listvyanka settlement (E. coli in 4 times, enterococci in 4.7 times), Chivyrkuy Bay (E. coli in 5.2 times, enterococci in 6.4 times) and Maloe More (enterococci in 4-6 times). Six out of seven tributaries, the rivers Pereemnaya, Snezhnaya, Solzan and Goryachiy Klyuch, also had exceedance values, especially the Pokhabikha (OCB in 11 times, E. coli in 58 times, Enterococci in 186 times) and the Medlyanka (OCB in 1.2 times, E. coli in 5 times, Enterococci in 63 times).

According to the results of analyses, the treated wastewater from the Slyudyanka wastewater treatment plant does not meet the requirements of SanPiN 1.2.3685-21 and exceeded the following indicators (OCB in 4200 times, E. coli in 17000 times and Enterococci in 3600 times), which indicated the absence of disinfection stages. Similar results were obtained for the treated waste water from the waste water treatment plant in the Severobaikalsk town in 2022. Studies of 10 samples of coastal sandy sediments from different areas of Lake Baikal were characterized by different degrees of contamination with sanitary-indicative bacteria and enabled these areas to be classified into three groups according to the degree of epidemiological hazard:

1. extremely dangerous – the Slyudyanka town;
2. dangerous – the Kultuk, Maksimikha, Kurbulik, and Sakhyurta settlements, Aya and Zmeinaya bays;
3. moderately dangerous – the Baikalsk town, Khuzhir and B. Koty settlements.

Studies of the surface water in the pelagic zone of Lake Baikal both in previous years and in this period correspond to the norms of SanPiN 1.2.3685-21 and MUK 4.2.1884-04 “Sanitary-microbiological and sanitary-parasitological analisis of water in surface water bodies”, with single exceptions of samples for the number of OCB in 2011-2012, 2015, 2019, 2021-2022.

A collection of 172 cultured opportunistic bacterial strains isolated from the Lake Baikal plankton, epilithon, treated wastewater and coastal sediments of the lake was created. Sixty-two strains isolated from biofilms and surface water samples were analyzed by modern identification methods (molecular-genetic and mass-spectrometry analyses) (Shtykova et al., 2018a; Shtykova et al., 2020). A total of 18 genera and 21 species of opportunistic bacteria were identified by this method. Among them are representatives of the order Enterobacterales of the genus Yersinia, Citrobacter, Escherichia, Hafnia, Leclercia, Lelliottia, Enterobacter, Shigella, of the order Pseudomonadales of the genus Pseudomonas, Acitrobacter, of the order Bacillales of the genus Bacillus, Exiguobacterium and Staphylococcus, of the family Aeromonadaceae of the genus Aeromonas, of the family Enterococcaceae of the genus Enterococcus, of the family Aerococcaceae of the genus Aerococcus, family Comamonadaceae of the genus Delftia, of the family Xanthomonadaceae of the genus Stenotrophomonas.

Species of opportunistic bacteria dangerous for human and animal health were isolated from different places throughout littoral zone of Lake Baikal. Thus, bacteria of the genus Aeromonas are the most widespread, were found in Maloe More Strait in Bazarnaya Bay and in Khuzhir-Nagaysky Bay, in Khool Bay, near the Khuzhir, Listvyanka settlements, B. Koty, and B. Goloustnoye settlements, and in Aya Bay. Bacteria of the genus Enterococcus are found in many bays of Maloye More. The strains of E. coli were detected in different water areas of the lake – in bays of Mukhor and Khool, near the settlement of B. Koty, and near the Ushkan Islands. We took into account that from 2022, according to new changes in SanPiN 1.2.3685-21, E. coli bacteria and enterococci are obligatory indicators in the sanitary-microbiological assessment of water quality.

In 2021-2023, wastewater samples were taken after the treatment facilities in the Slyudyanka and Severobaikalsk towns, low efficiency of disinfection and inflow of opportunistic and pathogenic bacteria into Lake Baikal were revealed (Potapov et al., 2023). Seventy bacterial strains isolated from water and 17 strains from wastewater treated at Slyudyanka treatment plant were subjected to antibiotic sensitivity tests, and the results revealed antibiotic resistance to all tested broad-spectrum antibiotics used to treat infectious diseases (penicillins, cephalosporins, carbapenems, macrolides, aminoglycosides, tetracyclines, nitrofurans, etc.).

4. Conclusion

Analysis of the results of sanitary-bacteriological monitoring for the previous and present centuries clearly indicates a decrease in water quality in the coastal zone of Lake Baikal, as well as in the tributaries of its southern basin: the number of OCB, TCB, and enterococci has increased, exceeding the requirements of SanPiN 1.2.3685-21. Over the last decade, an increase in the number of enterococci was seen in the lake`s deep-water area. The results obtained indicate that untreated or insufficiently treated wastewater flows into the rivers and the lake itself. According to sanitary-microbiological analyses, the Slyudyanka and Severobaikalsk wastewater treatment plants were inefficient during the studied period. Wastewater from the outlet pipes of the waste water treatment plants did not meet the requirements of SanPiN 1.2.3685-21, the number of coliform bacteria exceeded the normative values. A collection of 172 culturable opportunistic bacteria isolated from the Lake Baikal water, treated waste water and coastal sediments of the lake was created.

We propose the “Scheme of sanitary-bacteriological monitoring” as a result of the analysis of long-term studies of sanitary-indicative microorganisms in Lake Baikal, which calls for the determination of the water quality of the littoral and pelagic parts to be done throughout the year in all four seasons: winter (March), spring (late May-early June), summer (August), and autumn (late September-early October) (Fig. 3). The problem of preserving high-quality water is of great practical importance for Lake Baikal, which contains 20% of all fresh water on Earth, at the current time of global warming and increasing anthropogenic (biological and chemical) impact; regular sanitary-bacteriological monitoring will rapidly and reliably show trends in the trophicity of its ecosystem. The obtained data confirm that the waters of Lake Baikal are subjected to an intensive anthropogenic load, which has been steadily increasing in recent years. The distribution of FIB has an irregular, local character, caused by localization to the places of anthropogenic influence on the lake, which is also confirmed by the results of chemical analysis of the waters. The maximum number of sanitary-indicative bacteria is observed in the estuaries of rivers, gradually decreasing as the river water spreads into the lake. Based on the results of recent studies, it is suggested that under the influence of anthropogenic factors in coastal zones, there is a shift of autochthonous microbiota towards allochthonous microbiota characterized by high resistance to antibiotics. The introduction of antibiotic-resistant strains into environmental objects maintains the pool of resistant strains due to the transfer of resistance genes among autochthonous bacterial communities in the ecosystem. The transfer of antibiotic resistance genes into communities has received worldwide attention. The spread of such genes among bacteria is known to increase morbidity and mortality from the infections they cause. If there are additional factors contributing to the persistence and multiplication of PPB and if there are no community treatment facilities, the self-cleaning capacity of the lake coastal waters may be reduced to such an extent that their use becomes epidemiologically unsafe. This requires the development of a water quality management strategy for Lake Baikal.

 

Fig.3. The scheme of sanitary-bacteriological monitoring of Lake Baikal. River stations: 1 – Goloustnaya, 2 – Bugul’deika, 3 – Anga, 4 – Kuchulga, 5 – Sarma, 6 – Rel’, 7 – Tyya, 8 – Kichera, 9 – V. Angara, 10 – Tompuda, 11 – Barguzin, 12 – Turka, 13 – Selenga, 14 – Mysovka, 15 – Pereemnaya, 16 – Snezhnaya, 17 – B. Osinovka, 18 – Solzan, 19 – Slyudyanka, 20 – Pokhabikha, 21 – Kultuchnaya, 22 – Medlyanka. Pelagic stations: 1 – 12 km from Kultuk, 2 – 3 km from Maritui, 3 – Maritui‒Solzan, 4 – 3 km from Solzan, 5 – 3 km from Listvyanka, 6 – Listvyanka–Tankhoi, 7 – 3 km from Tankhoi, 8 – Krasnyi Yar–Kharauz, 9 – Anga‒Sukhaya, 10 – Boldakova–Malye Olkhonskie vorota, 11 – 3 km from Ukhan, 12 – Ukhan–Tonkiy, 13 – 3 km from Tonkiy, 14 – 7 km from Izhimei, 15 – Khoboi–Krestovyi, 16 – Barguzin Bay, 17 – Academicheskiy Ridge, 18 – Chivyrkui Bay, 19 – Solnechnaya–Ushkanyi Islands, 20 – Zavorotnyi–Sosnovka, 21 – 3 km from Elokhin, 22 – Elokhin–Davsha, 23 – 3 km from Davsha, 24 – Kotelnikovskiy–Amnundakan, 25 – 3 km from Baikalskoe, 26 – Baikalskoe–Turali, 27 – 3 km from Turali, 28 – Tyya–Nemnyanka, 29 – 7 km from Nizhneangarsk, 30 – Aral–Khoboy, 31 – Maloye More Strait, 32 – Malye Olkhonskie vorota. Coastal stations: 1 – Listvyanka, 2 – B. Koty, 3 – B. Goloustnoe, 4 – Peschanaya Bay, 5 – Aya Bay, 6 – Tutaiski Bay, 7 – Bazarnaya Bay, 8 – Shchuchiy Bay, 9 – Radost‘ Bay, 10 – Kurkut Bay, 11 – Burlyuk Сape, 12 – Chukotka Bay, 13 – Mandarkhan Bay, 14 – Zuun-Khagun Bay, 15 – Baruun-Khagun Bay, 16 – Shida Bay, 17 – Ulirba Сape, 18 – Khuzhir-Nugai Bay, 19 – Sarma, 20 – Mukhor Bay, 21 – Irkutskaya guba Bay, 22 – Tutyrkhey Bay, 23 – Kharin-Irgi Bay, 24 – Khool Bay, 25 – Khytyrhey Bay, 26 и 27 – Zagli Bay, 28 – Khuzhir, 29 – Elokhin Сape, 30 – Severobaikalsk, 31 – Frolikha Bay, 32 – Аyaya Bay, 33 – Khakusy Bay, 34 – Monakhovo, 35 – Kurbulik, 36 - Zmeinaya Bay, 37 – Peshcherka Bay (Ushkany Islands), 38 – Maksimikha, 39 – Turka, 40 – N. Enkhaluk, 41 – Posol’skiy sor, 42 – Babushkin, 43 – Tankhoi, 44 – Vydrino, 45 – Baikalsk, 46 – Slyudyanka, 47 – Kultuk. Termal springs stations: 1 – Khakusy, 2 – Zmeinyy.

 

Acknowledgements

The study was carried out within the State Task No. 0279-2021-0015 (121032300269-9).

Conflict of interest

The authors declare that they have no competing interests.

About the authors

V. V. Drucker

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

M. Yu. Suslova

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

Yu. R. Nebesnykh

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

S. A. Potapov

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

G. V. Podlesnaya

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Author for correspondence.
Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

O. I. Belykh

Limnological Institute of the Siberian Branch of the Russian Academy of Sciences

Email: podlesnaya@lin.irk.ru
Russian Federation, Ulan-Batorskaya Str., 3, Irkutsk, 664033

References

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